J.C. Viala

Bio: J.C. Viala is an academic researcher from Claude Bernard University Lyon 1. The author has contributed to research in topics: Alloy & Aluminium. The author has an hindex of 15, co-authored 35 publications receiving 537 citations.

Interface chemistry in aluminium alloy castings reinforced with iron base inserts

Abstract: Bimetallic automotive components consisting of an Al–Si light alloy reinforced with a cast iron insert have been manufactured by gravity die moulding. Special precautions have been taken to ensure a uniform wetting of the insert by the liquid light alloy. Under these conditions, three intermetallic compounds are formed at the insert/alloy interface: η (Al 5 Fe 2 ), τ5 (Al 7.4 Fe 2 Si) and τ6 (Al 4.5 FeSi). Upon subsequent heat-treatment, τ2 (Al 5 Fe 2 Si 2 ) and τ10 (Al 12 Fe 5 Si 3 ) also appear. Growth of these compounds is discussed in terms of thermodynamics, kinetics and reaction mechanism in the Al–Fe and Al–Fe–Si systems. The effect of these chemical changes on the mechanical properties of the insert/alloy joint will be examined.

Solid-liquid phase equilibria in the Al-Fe-Si system at 727 °C

Abstract: Different experimental techniques were combined to acquire better insight into the solid-liquid phase equilibria that tend to be established in the Al-Fe-Si ternary system at 727 °C under a pressure of 1 atm (101,350 Pa). Isothermal diffusion experiments followed by oil quenching were first carried out. The crystal nature, lattice parameters, morphology, and chemical composition of the different solid phases in equilibrium with the liquid were determined by x-ray diffraction, optical microscopy, scanning electron microscopy, and electron probe microanalysis. Points on the liquidus boundary were then positioned both directly by chemical analysis of liquid samples taken from solid-liquid mixtures equilibrated at 727 °C and indirectly by thermal analysis of Al-Si mixtures with controlled iron additions. On the one hand, it has been confirmed in agreement with currently accepted data that the compounds ϑAl13Fe4, αAl7.4Fe2Si (τ5), and δAl3FeSi2 (τ4) are in equilibrium at 727 °C with Al-Fe-Si liquids, the compositions of which have been refined. On the other hand, the authors have shown that the ternary compound γAl3FeSi is in equilibrium at 727 °C with a ternary Al-Fe-Si liquid containing 10.5 to 16.5 at.% Si and 3.2 to 3.5 at. % Fe.

Low-Temperature Interface Reaction Between Titanium and the Eutectic Silver-Copper Brazing Alloy

Abstract: Reaction zones formed at 790 °C between solid titanium and liquid Ag-Cu eutectic alloys (pure and Ti-saturated) have been characterized. When pure Ag-Cu eutectic alloy with 40 at.% Cu is used, the interface reaction layer sequence is: alpha-Ti / Ti2Cu / TiCu / Ti3Cu4 / TiCu4 / L. Because of the fast dissolution rate of Ti in the alloy, the reaction zone remains very thin (3-6 µm) whatever the reaction time. When the Ag-Cu eutectic alloy is saturated in titanium, dissolution no longer proceeds and a thicker reaction zone with a more complex layer sequence grows as the reaction time increases. Four elementary chemical interaction processes have been identified in addition to Ti dissolution in the liquid alloy. These are growth of reaction layers on Ti by solid state diffusion, nucleation and growth from the liquid of TiCu4, isothermal solidification of silver and, finally, chemical conversion of the Cu-Ti compounds by reaction-diffusion in the solid state. A mechanism combining these processes is proposed to account for the constitution of Ti/ Ag-Cu/ Ti joints brazed at 780-800 °C.

Affinement expérimental de l'isotherme Al-Fe-Si à 1000 K

Abstract: With more than fifteen reported stable binary and ternary compounds, the Al-Fe-Si phase diagram is rather complex. To get a better insight into that diagram, experiments were carried out by isothermal diffusion and thermal analysis. The results of these experiments have been combined with previous data to provide a refined Al-Fe-Si section at 1000 K.

Nanoscaled metal borides and phosphides: recent developments and perspectives

Abstract: and Perspectives Sophie Carenco,†,‡,§,∥,⊥ David Portehault,*,†,‡,§ Ced́ric Boissier̀e,†,‡,§ Nicolas Meźailles, and Cleḿent Sanchez*,†,‡,§ †Chimie de la Matier̀e Condenseé de Paris, UPMC Univ Paris 06, UMR 7574, Colleg̀e de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France ‡Chimie de la Matier̀e Condenseé de Paris, CNRS, UMR 77574, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Chimie de la Matier̀e Condenseé de Paris, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Laboratory Heteroelements and Coordination, Chemistry Department, Ecole Polytechnique, CNRS-UMR 7653, Palaiseau, France

Summary of constitutional data on the Aluminum-Carbon-Titanium system

Abstract: The constitution of the titanium-aluminum-carbon ternary system has been investigated combining critical evaluation of literature data with new experimental results. Three ternary phases occur in this system: Ti3AlC, Ti2AlC, and newly discovered Ti3AlC2. As analyzed by wet chemistry methods, all three phases are carbon deficient with respect to their “ideal≓ stoichiometry, which is based on the crystal structure formula. Ti2AlC and Ti3AlC melt incongruently at 1625 ± 10 ‡ and 1580 ± 10 ‡, respectively. Ti3AlC2 decomposes in the solid state. The two isothermal sections at 1000 and 1300 ‡ investigated experimentally are corroborated by thermochemical calculations. A projection of the liquidus surface is given, and a reaction scheme linking this liquidus projection with the isothermal sections observed is proposed.

Chemical reactivity of aluminium with boron carbide

Abstract: The chemical reactivity of boron carbide (B4C) with metallic aluminium (Al) was studied at temperatures ranging from 900 to 1273 K (627–1000 °C). Al–B4C powder mixtures were cold pressed, heated for 1–450 h under 105 Pa of purified argon and characterized by X-ray diffraction (XRD) optical metallography (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Whatever the temperature in the investigated range, B4C has been observed to react with solid or liquid Al. As long as the temperature is lower than 933 K (660 °C), i.e. as long as Al is in the solid state, interaction proceeds very slowly, giving rise to the formation of ternary carbide (Al3BC) and to diboride (AlB2). At temperatures higher or equal to 933 K, Al is in the liquid state and the reaction rate increases sharply. Up to 1141 ± 4 K (868 ± 4 °C), the reaction products are Al3BC and AlB2: at temperatures higher than 1141 K, Al3 BC is still formed while Al3B48C2 (β-AlB12) replaces AlB2. In the three cases, interaction proceeds via the same mechanism including, successively, an incubation period, saturation of aluminium in B and C, nucleation and growth by dissolution–precipitation of Al3BC and a C-poor boride and, finally, the passivation of B4C by Al3BC. These results are discussed in terms of solid–liquid phase equilibria in the Al–B–C ternary system, with reference to the binary invariant transformation: α-AlB12 + L ⇔ AlB2, which has been found to occur at 1165 ± 5 K (892 ± 5 °C).